It is common practice to treat injured areas of the human body with a hot or cold compress as an aid in the healing process. Localized thermal transfer involves the application of cold or heat, either dry or moist, to a specific area of the body to provide one or more of the following therapeutic affects:
______________________________________ Cold Therapy Heat Therapy ______________________________________ Decrease Blood Flow Increase Blood Flow Decrease Edema Decrease Swelling Decrease Hemorrhage Prevent Tissue Encrustation Decrease Inflammation Promote Wound Drainage Decrease Muscle Spasm Decrease Muscle Spasm Decrease Pain Decrease Pain Provide Patient Comfort Provide Patient Comfort ______________________________________
The therapeutic indications for localized cold or heat therapy are extensive. Many conditions call for application of either modality depending on how soon the treatment is initiated. For example, in orthopedic cases, if treatment begins within the first 48 hours after the injury occurs, cold therapy is usually instituted. Thereafter, heat therapy is the preferred mode of treatment. Thermal therapy comprising applications of cold, heat or some combination of the two is useful for a variety of conditions including acute injuries, arthritis, bruises, cellulitis, chronic pain, low back pain, muscle spasm, post-op, sprains, strains, wounds, alopecia, abscesses, headaches, nose bleeds, burns, circulatory disorders, infection, IV infiltration, neuritis, phlebitis, and tendonitis.
In the past, heat has been applied using electric heating pads, hot packs, heat lamps, hot water bottles, hot towels or paraffin baths. Cold has been applied using ice bags, cold packs, cold compresses or cold water bottles. All of these have significant drawbacks, the most obvious being that of inadequate temperature control. This is especially true when extended sessions of treatment are required. A more convenient way of applying such a compress known in the prior art is with a flexible pad having internal passages through which is circulated a warm or cold fluid, usually water, by means of a pump. Typically, the pump assembly includes a reservoir for the liquid, a heater to warm the liquid when desired and means for selecting a desired temperature and maintaining the liquid at that temperature. When a cold compress is desired, the heater is switched off and the reservoir filled with ice water.
The fluid-circulating thermal therapy systems of the prior art also suffer from a number of problems. First, the thermal pads of the prior art fail to provide simultaneously the properties of a highly absorbant, non-slip, non-linting surface with good moisture retention for moist thermal therapy along with good wet strength and a lofty, cushioned feel in a material which is sanitary, relatively inexpensive and readily bonded to the underlying layers of the pad. Non-linting properties are particularly important since migration of fibers into a wound may cause a granuloma to be formed. Secondly, prior art systems fail to provide an indication of the actual temperature of the circulating fluid. Those that provide any temperature indication at all, show only the set-point temperature. They provide no means to determine whether the set-point has been reached or is being properly maintained. Accordingly, to protect the patient there is a need for a system that provide for monitoring the actual fluid temperature as well as the set-point. Third, it is desirable to prevent the patient or other unauthorized persons from altering the temperature set-point prescribed by a physician. According to the prior art this is accomplished by making the set-point adjustment means accessible by way of a key. This requires the nurse or other person in charge to carry the key which is of course subject to being lost or forgotten during a trip to the patient's room. Accordingly, there exists a need for a thermal therapy system which does not require a key but which nonetheless prevents unauthorized persons from altering the temperature set point. Fourth, the systems of the prior art fail to provide a means for directly sensing the water level in the area of the heater and de-energizing the heater when the water in that area drops below a safe level. Instead, these systems rely upon a thermostat to sense the resulting temperature rise in the area of the heater. This is undesirable because under conditions of a rapid temperature rise, such as when an immersion heater runs dry, a thermostat may permit a substantial overshoot in temperature before operating to interrupt power to the heater. Fifth, prior art fluid-circulating thermal therapy systems did not provide a means for de-energizing both the pump and the heater when the unit was tilted beyond a safe angle. Finally, prior art systems must be manually calibrated to insure that the indicated set-point temperature corresponds to the true temperature at which the fluid is being maintained. Calibration can change for a variety of reasons. As the electronic components associated with the temperature measurement and control functions age, their physical characteristics undergo gradual changes which affect the accuracy of temperature measurements. Perhaps more important than gradual aging are the rapid changes in characteristics these electronic components exhibit as the temperature and humidity of the environment in which they operate change. This is extremely significant in a fluid-circulating thermal therapy system since the temperature and humidity in the area where the electronics operate vary over the operating cycle of the unit. For example, when the system is first energized, the temperature and humidity within its housing are very close to the ambient conditions of the room in which the system is located. As the heater warms up, the temperature and humidity in the area of the electronic components rise over the period of an hour or so until they finally stabilize at a steady state.
Even if care has been taken to calibrate the unit after a long warm-up so it is accurate under stabilized conditions, the unit may operate with impaired accuracy for a significant period of time before steady state temperature and humidity are reached. Such inaccuracies cannot be corrected in units constructed according to the prior art since they are not addressed by a routine calibration performed under steady state conditions. Accordingly, there is a need for a fluid-circulating thermal therapy system which calibrates itself at intervals frequent enough to account for changes in calibration occurring as the result of changes in the internal operating environment of the unit during its operating cycle as well as over a period of months or years.